Useful Notes / Prehistoric Life - Ankylosaurs

Frequently-portrayed North American ankylosaurs include the club-less Nodosaurus, Sauropelta, Edmontonia, and (more recently) Gastonia. The European Polacanthus and Hylaeosaurus have been common sights as well because of their historical relevance, while Pinacosaurus is the most-often seen Asian ankylosaur, followed by Saichania. Among kinds found in other continents you might see Minmi from Australia. The placement of the primitive Scelidosaurus as an ankylosaur is still controversial: we've put it in this page because is ankylosaur-looking, but could alternatively be placed in the Primitive Ornithischians as well.

Humble origins: Hylaeosaurus

Huge Ankylosaurus has not always been THE ankylosaur. Was discovered at the beginning of the XX century, but several relatives were already known. They were simply smaller, less-armored and, above all, very fragmentary, and in the XIX were classified among the Stegosaurs. As a group, the Ankylosauria were recognized distinct only after Ankylosaurus.

In fact, one of the three inspirers of the name “dinosaur” was an ankylosaur: Hylaeosaurus. Discovered in England in 1840, was only 4 m long and with very partial remains (as every “early” dino-discover). In famous Crystal Palace Park in London, the hylaeosaur shows up with the more-known Megalosaur and Iguanodont… but is sculpted like a giant, armor-less iguana.

Spiny yet clubless: Polacanthus

Some decades later, a companion was added to Hylaeosaurus: Polacanthus. English too, and also conviving with Iguanodon in the Early Cretaceous, it was also 4 m long, and also very incomplete. In older depictions, Polacanthus had very light armor, consisting only of pairs of long dorsal spikes (hence the name, "many spines"), a bony shield on its hips, and small plates on the tail. Some portrayals took it a further step and gave it a stegosaur-like thagomizer. The spiked-tailed polacanth made cameo appearances in Planet of Dinosaurs and the film adaptation of The Land That Time Forgot as well as a more prominent role in Dinosaurs as Robbie Sinclair's friend Spike. Today we know its armor was extensive and Ankylosaurus-like (though even spikier) and with no club-like tail. The polacanth appears with this new look in Walking with Dinosaurs as a follower of Iguanodon herds.

Spiny little guys: Acanthopolis & Struthiosaurus

The other ankylosaurs found in Europe are usually like those cited above: small, fragmentary and clubless. To compensate, some are very coolly-named. Acanthopholis almost seems “Polacanthus” inverted. Struthiosaurus means “Ostrich-Lizard” (making thinking it was Struthiomimus-like…). Dracopelta is the “armored dragon”. But the weirdest-named is Sarcolestes: “meat thief”.

Both Dracopelta and Sarcolestes were Jurassic (the latter was one of the first proper ankylosaurs to have evolved), while Acanthopholis was an Early Cretaceous ankylosaur found in England in the XIX century and known from very scant remains, just like Hylaeosaurus. Struthiosaurus is far more interesting. It is one of the smallest known quadrupedal dinosaurs (the size of a dog), and was one of the several dwarf dinosaurs that decreased their size to survive in the islets of the Late Cretaceous Europe. Struthiosaurus makes also a striking example of I Have Many Names: its remains (found in several European countries, among them Transilvania) were once classified in more than six genera. A recent found (2005) is Hungarosaurus from Hungary: another inhabitant of the Late Cretaceous islets, it was the most complete European ankylosaur until the discovery in Spain of the Early Cretaceous Europelta, made in 2013.

Ankies conquer the USA: Nodosaurus & "Palaeoscincus"

Even in Usa the first dino-discoveries included an ankylosaur, one even more incomplete than Hylaeosaurus: “Palaeoscincus” was descibed in 1856 from isolated teeth initially believed from a lizard. Many undetermined remains were later assigned to it, making “Palaeoscincus” a Waste-Basket taxon, but now they are either regarded as dubious, or classified in other genera. The images of "palaeoscincus"es often seen in old dino-books are actually based upon another better-known ankylosaur, Edmontonia (see below).

The first North-American ankylosaur known from decent remains was Nodosaurus. Described during the Bone Wars, was known only from pieces of armor with no spikes: that’s why, in old portraits, Nodosaurus appears spikeless. It became the prototype of its own family, the Nodosaurids, in which every club-less ankylosaur used once to be put.

Spiny big guys: Edmontonia & Panoplosaurus

More complete nodosaurids appeared in the XX century, and showed very spiky bodies: Panoplosaurus and Edmontonia (so-called because was found near Edmonton in Canada, see also Edmontosaurus). Both were large (6 m or so) with a complex armor expecially in the frontal portion of their body. Edmontonia in particular showed huge shoulder-spikes often double pointed.

Nevertheless, Edmontonia and Panoplosaurus were also narrow-headed and devoid of horns or tail-clubs, like all nodosaurs. In 1988, famous paleontologist Bob Bakker described a shattered skull which has later revealed to be from Edmontonia. Named “Denversaurus” from the capital of Colorado (Bakker’s state), it might have given its name to the hero of a famous TV dino-cartoon broadcast just in those years.

The Pelta Family: Sauropelta

All the nodosaurs above were Late Cretaceous like Ankylosaurus. In the 1970s, Ostrom described an Early Cretaceous animal from Montana, Sauropelta: Ostrom wasn’t aware of, but started the trend to name ankylosaurs with the suffix –pelta: Aletopelta, Cedarpelta, Mymoorapelta, and others, all found later than the ur-example (see further). Also North American and Early Cretaceous were Silvisaurus and Pawpawsaurus, smaller relatives. The name Silvisaurus means "forest lizard" — the same meaning of Hylaeosaurus, but with a Latin root instead of Greek (similarly to the couple of names Ornithomimus & Avimimus). While Pawpawsaurus is not a reference to the fruit, but to the formation it was dug out.

With its 7.5 long body, Sauropelta was the biggest nodosaurid known, had long lateral spikes (expecially long on the shoulders) but a simpler armor on its back than its Late Cretaceous relatives, with small mosaic-like scutes of different size. All nodosaurids had mosaic-like armor, very different to that of the ankylosaurids, made by wide rows put in line on the upper body. Found only in 2008 is another Early Cretaceous nodosaur from Utah, Peloroplites ("monstrous soldier"), which is only a bit smaller than Sauropelta.

Club or spikes?: Scolosaurus

It seems Science Marches On can potentially hit every well-known dinosaur, suddenly making it less relevant than it used to be. Late Cretaceous North America has several example of dinosaurs that were very common in older popular dino-books but now have been "substituted" in their role by close relatives. The carnivorous Gorgosaurus was synonymized with Albertosaurus between the 1970s and the 2000s (though this has been reversed, and it is now a valid genus again); the hadrosaur Kritosaurus was revealed to be based upon the related Gryposaurus in the 1990s; the ceratopsid Monoclonius is today thought by several experts as a non-diagnostic juvenile centrosaur; and the small deinonychosaur Stenonychosaurus has been synonimized with Troodon since the 1980s. And, of course, the notorious "Trachodon" case.

The couple Scolosaurus/Euoplocephalus is the latest addition in this special list. The original specimen of the latter was discovered in 1902. Between 1923 and 1929 three other genera very similar to it (Dyoplosaurus, Scolosaurus, and Anodontosaurus) were named, but these three were combined into Euoplocephalus in 1971. However, all three genera were rescued from the Invalid Box between 2007 and 2013 after showing that some patterns of armor were useful in classifying their owners. For example, the Dyoplosaurus club was different from that of Euoplocephalus, being longer than wide, while the Anodontosaurus club had pointed ends like a giant pickaxe. Dyoplosaurus was also older than most Euoplocephalus specimens, while Anodontosaurus lived after the latter but before Ankylosaurus.

But it's Scolosaurus that has surely been the most relevant among these alleged euoplocephaluses. It is known from one really well-preserved skeleton from Alberta and several more incomplete specimens from Montana note . The scolosaur was about the same size as Euoplocephalus, live in the same age, had a similar head but with longer, more swept-back horns, and a club also similar in shape. The main point is: the aforementioned "artistic" armor has been found to actually pertain to Scolosaurus, while the real Euoplocephalus had less complex armor. The classic "Euoplocephalus" portrayals are actually based on the aforementioned well-preserved Scolosaurus found in Alberta.

This skeleton, nonetheless, lacked the skull as well as the clubbed tip of its tail, making its tail look shorter and ending with a single pair of spikes (which were actually in the middle of the tail). Several old books and models have portrayed this "stegosaur-tailed ankylosaur" (wrongly showing it with much more generic armor than the Real Life fossil): interestingly, they usually named it "Scolosaurus" instead of "Euoplocephalus", but sometimes they wrongly named it "Ankylosaurus" (ex. one famous picture by Zdenek Burian which shows this critter defending itself against a Gorgosaurus). Though few noticed, even one very popular work has made the same mistake: if observed carefully, the wise "Euoplocephalus" Rooter has armor analogous to Knight's picture, and also shows the pair of spikes on the tip of its tail when he goes away, revealing it's based on a very inaccurate, old-fashioned Scolosaurus.

Prickly loners, or playful youngsters?: Pinacosaurus

Many more ankylosaurids are known from Asia, mostly from Late Cretaceous: Pinacosaurus, the most common in fossil record, was basically the equivalent of Euoplocephalus and Scolosaurus. Smaller than them and with a much simpler armor, Pinacosaurus had also a narrower head and a hooked bill. The less-common Tarchia and Saichania were more similar to Ankylosaurus; Talarurus was hippo-shaped and short-limbed; while Shamosaurus and Gobisaurus were primitive Early Cretaceous forms (the name of both meaning "lizard from the Gobi Desert"). Very little-known are other two ankies from China, Sauroplites and the deceptively-named Stegosaurides.

First found in 1920s, Pinacosaurus has been the first armored dinosaur found in Asia. It has left in the eighties a proof of social behavior among ankylosaurs (traditionally considered loners): several youngsters found dead together in a small area, maybe buried in a sandstorm. Talarurus was of middle-size, and was the second Asian ankylosaur discovered after Pinacosaurus. It has surprisingly appeared in Disney's Dinosaur, although only with a simple cameo.

Smart and beautiful: Tarchia & Saichania

Both Tarchia and Saichania were found in the 1970s. 8.5 m long, Tarchia is the biggest described Asian ankylosaur, almost as large as Ankylosaurus; Saichania too was very large (7 m). Both ankylosaurs have rather funny names: Tarchia means “brain” and Saichania means “beautiful” (a reference to the beauty of its well-preserved skeleton).

Though not described yet, "Hanwulosaurus" could actually be the biggest Asian ankylosaur (9 m long). Also interesting is Minotaurasaurus (the "minotaur dinosaur", found only in 2009), similar to Tarchia & Saichania but with unusually-long "horns".

The Unfair Sex: Gastonia

Since the 1990s, the classic “nodosaurid” / “ankylosaurid” bipartition has fallen down: many nodosaurids have revealed not to be related with Sauropelta or Edmontonia. Among them, the “polacanthines”: the European Polacanthus & Hylaeosaurus and the obscure Hoplitosaurus, known since the start of the XX century from scanty North American remains from Early Cretaceous. Some think polacanthines were closer to nodosaurids than to ankylosaurids, but others don't agree.

Just in the 1990s new, more complete polacanthines were found in USA. The first one, following the trend to name ankylosaurs with –pelta, was called Mymoorapelta in 1993: this one was the first North American ankylosaur from Late Jurassic, and lived alongside Stegosaurus Allosaurus Diplodocus etc. Also from the same fauna was the coolly-named Gargoyleosaurus, found in 1998. Aletopelta and Cedarpelta (both found in the early 2000s) lived in the Cretaceous North America. They are considered primitive ankylosaurids but share also resemblances with polacanthines, leading some thinking the latter were closer to club-tailed ankylosaurs than to proper nodosaurs.

The most striking polacanthine was described in 1998 like Gargoyleosaurus, but comes from Early Cretaceous, the Utahraptor age: Gastonia. Still another ankylosaur with the name ending in -a. Indeed this is the dino group with the greatest number of names ending so, giving them a bizarre “feminine” sound for these bulky “tanks”... Found in 1998 as well, Gastonia impressed researchers because of its armor, filled with long spikes pointing to all directions. Some people have hailed it as the most armored animal ever existed on Earth: in short, a perfect opponent for the neighboring Utahraptor. Indeed, Gastonia fights the giant dromeosaurid in the Jurassic Fight Club, and ends the battle as the victory.

Naming questions: Minmi & the "Antarctic ankylosaur"

Despite this example, non-stock ankylosaurs (and stegosaurs) are usually ignored in visual media. Maybe their reputation of “slow and foolish” has done its part, even though this fame is undeserved. A good example of missed opportunity was a small ankylosaur discovered in Australia, with one of the least dinosaurian name one could imagine: Minmi. note  Discovered in 1980, this is the most complete Australian dinosaur to date, and yet it does not appear in the Walking with Dinosaurs episode "Spirits of the Ice Forest", in which the much less-complete Leaellynasaura and even the “polar allosaur” appear (despite being their contemporary).

Once considered nodosaurid, today Minmi is thought a primitive, hard-to-classify ankylosaur, perhaps with some bony plates even in its belly (a rare thing among ankylosaurs). It was also the first ankylosaur ever found in the southern emisphere, but was steadily reached by a second animal in 1986, another primitive ankylosaur, this time discovered in Antarctica. This one was the very first dinosaur ever discovered in the Ice Continent, yet has had to expect twenty years to be named: Antarctopelta.

Nonetheless, the most awesome case regarding naming questions comes from Jurassic China: “Jurassosaurus nedegoapeferima”. Found in the early 1990s (when the Jurassic Park-mania began), the first term is a straight omage to Spielberg; the other is formed from the surnames of the film's main stars: Sam Neill, Laura Dern, Jeff Goldblum, Sir Richard Attenborough, Bob Peck, Martin Ferrero, Ariana Richards, and Joseph Mazzello. Even though the genus is now known as Tianchisaurus, it still keeps its bizarre species name. As it was not enough, another asian ankylosaur was in 2002 named Crichtonsaurus for Michael Crichton. Well, it’s true, ankylosaurs really have some of the most awesome names within the dinosaur world.

The outsider: Scelidosaurus

When we think about armor-bodied dinosaurs, our minds comes to stegosaurs and ankylosaurs. But let’s not forget Scelidosaurus: a very primitive, thyreophoran from Early Jurassic, discovered in Europe and possibly North America.

Only 4 m long (half the length of an average Stegosaurus and small also for ankylosaurian standards), it was traditionally considered in the middle between stegosaurs and ankylosaurs, but some have recently suggested that it's the first true ankylosaur. Still, Scelidosaurus was more slender and far less armored than traditionally-indended ankylosaurs. Its armor was made only of small bony tubercles sparse along its body, while its small head had not a bony “cap” but just three short spikes on each rear-corner. Its limbs were more similar to bipedal ornithischians than to ankylosaurs, note  and some scientists have hypothesized it was at least partially bipedal.

Scelidosaurus is a very early find among dinosaurs - its first skeleton is known since the XIX century even before Stegosaurus and Ankylosaurus have been known to science. Like most of the others earliest dino-discoveries, it was found in England. Having a not-so-impressive appearance Scelidosaurus has remained a non-stock animal. However, basal dinosaurs from Triassic and Early Jurassic often make paleontologists happier than their Late Jurassic or Cretaceous ones, because the most ancient dinosaurs help to understand a lot the affinities among the main dinosaurian groups, enhancing the reconstruction of their evolution.